CHAP. VI. STEPHENSON'S SECOND LOCOMOTIVE. 103 



a substitute, which, although less simple and efficient 

 was within the mechanical capabilities of the workme 

 of that day, in respect of construction as well as repair 

 He adopted a chain which rolled over indented wheel 

 placed on the centre of each axle, and was so arrange 

 that the two pairs of wheels were effectually coupled an 

 made to keep pace with each other. The chain, how 

 ever, after a few years' use, became stretched ; and then 

 the engines were liable to irregularity in their working, 

 especially in changing from working back to working 

 forward again. Eventually the chain was laid aside, 

 and the front and hind wheels were united by rods on 

 the outside, instead of by rods and crank axles inside, as 

 specified in the original patent. This expedient com- ' 

 pletely answered the purpose required, without involving 

 any expensive or difficult workmanship. 



Thus, in the year 1815, Mr. Stephenson, by dint of 

 patient and persevering labour, by careful observation 

 of the works of others, and never neglecting to avail 

 himself of their suggestions, had succeeded in manu- 

 facturing an engine which included the following 

 important improvements on all previous attempts in the 

 same direction : viz., simple and direct communication 

 between the cylinders and the wheels rolling upon the 

 rails ; joint adhesion of all the wheels, attained by the 

 use of horizontal connecting rods ; and finally, a beautiful 

 method of exciting the combustion of the fuel by 

 employing the waste steam, which had formerly been 

 allowed uselessly to escape into the air. Although . 

 many improvements in detail were afterwards introduced / 

 in the locomotive by Mr. Stephenson himself, as well as j 

 by his equally distinguished son, it is perhaps not too i 

 much to say that this engine, as a mechanical con- 1 

 trivance, contained the germ of all that has since bee^i/ 

 effected. It may in fact be regarded as the type of tlie| 

 present locomotive engine. 



